Contactless pressurizing-gas shaft seal

ABSTRACT

A high pressure sealing arrangement of the type in which a rotor sealing ring end face generates a gas pressure with a stator sealing ring end face at a functional gap between a cylindrical portion of the seal housing and the stator sealing ring bridged by an O-ring of reduced hardness. The gap width is less than 0.4 mm and preferably less than 0.3 mm. The sealing O-ring additionally serve as a compensation or centering ring and has a material hardness which is greater than the extrusion threshold of this material through the gap and is less than a hardness of 90 Shore A according to German Industrial Standard DIN 53505. Preferably the hardness of the O-ring is less than 80 Shore A under this Standard.

CROSS REFERENCE TO RELATED APPLICATIONS

This application being filed is: a division of Ser. No. 07/971,150 filedNov. 3, 1992 (now U.S. Pat. No. 5,368,314 granted Nov. 29, 1994); whichis a C-I-P of Ser. No. 07/869,218 filed Apr. 13, 1992 (now abandoned);which is a continuation of Ser. No. 07/622,866 filed Dec. 5 1990 (nowabandoned); which is a C-I-P of Ser. No. 07/491,664 filed Mar. 9, 1990(now U.S. Pat. No. 5,092,612 granted Mar. 3, 1992;) which is a C-I-P ofSer. No. 115,063 filed Oct. 28, 1987 (now abandoned).

FIELD OF THE INVENTION

Our present invention relates to a gas-pressurizing and gas-blockingcontactless seal for a shaft and is adapted to be disposed between theshaft and the housing to block fluid passage therebetween whilemaintaining a sealing gap which has only gas pressure bridging betweenthe sealing ring elements which are relatively rotatable.

BACKGROUND OF THE INVENTION

A gas-blocking contactless seal for a shaft can comprise a sealinghousing surrounding the shaft, a stator seal ring disposed in thehousing and a rotor sealing ring mounted on the shaft.

The two sealing rings have juxtaposed end faces separated by the sealinggap in which the relative rotation of the rings generates a gas pressuresufficient to seal between the housing and the shaft.

As described, for instance in U.S. Pat. 5,092,612, for example, therotor sealing ring can be composed of a material of a high thermalconductivity and high modulus of elasticity as well as of high hardness.The sealing gap can be defined between the stator sealing ring and arotor sealing ring so that a predetermined operating differentialpressure is generated across the gap in the operating state of the seal,i.e. upon rotation of the shaft at its operating speed, and the statorsealing ring can be biased by a spring against the force of the sealingpressure while a rubber or plastic O-ring can seal between the statorsealing ring and a cylindrical portion of the sealing housing whichextends coaxial with and parallel to the shaft.

With such a sealing arrangement it is important to distinguish betweenthe functional annular gap, i.e. the gap between the cylindrical portionand the stator ring, and the mounting ring gap or tolerance, i.e. thegap or clearance which is provided to enable, for example, the statorring to be mounted.

The functional gap is developed out of the mounting ring gap by a kindof displacement in the mounted condition by the effect of the sealingoperating pressure differential.

It will be understood that there are various constructions of prior artsystems which utilize this approach to seal around a shaft. Some ofthese systems date back to 1925 and a variety of materials having therequisite hardness for such sealing systems is described, for example,in VDI Zeitschrift 102 (1960) No. 18, pages 728 to 732.

In one sealing arrangement of the aforedescribed type (see EuropeanPatent Publication EP 0013678) the recesses of the sealing rings whichgenerate the pressure gradient are spiral grooves which extend from aperipheral edge of the respective sealing ring. In this case, only therotor sealing ring is composed of a material of high thermalconductivity, modulus of elasticity and hardness.

The stator sealing ring is composed of a material of relatively lowmodulus of elasticity and minimal hardness, for example, of carbon,whose thermal conductivity is not significant.

Because of the relatively low modulus of elasticity and thermalconductivity of the thermal stator ring, this prior art sealingarrangement can give rise to a torsional deformation (twist) of thesealing assembly at least partially as a consequence of the operatingtemperature and this, in turn, can result in a cocking of one of therings.

The temperature gradient in the axial direction can in such cases be 25°C. or more. The torsional deformation of the stator sealing ring candetrimentally affect the seal formed during operation, can result incontact at inappropriate times between the sealing rings and can bedisadvantageous for a variety of other reasons.

It has been proposed to overcome the problem by counteracting thetorsional deformation moment, twist or torque by a moment or torquegenerated by an appropriate pressure distribution in the sealing gap sothat the two torques are effective in opposite senses. For this purpose,the recesses are formed as spiral grooves which are designed to have apumping effect at least for the spiral grooves formed in the rotorsealing ring and these grooves can extend inwardly toward the oppositeinner periphery from one of the inner peripheries of the annular sealingsurface. These grooves can end in a dam or rib so that the groove is notthroughgoing from one peripheral edge to the other. As a function of thespiral groove depth and the intergroove rib width as well as a functionof the equilibrium between the various parameter, it is possible tocreate the torque balance desired wherein the torsion effect iscounterbalanced by the torque or moment generated by the gas pressure.

Even when these conditions are scrupulously observed, the desired effectcannot always be achieved or the effect which is obtained can beunsatisfactory. For example, the described equilibrium cannot beobtained under all operating conditions. In practice, the planeparallelity of the confronting sealing surface can be restored only to amaximum of about 70%.

The problem appears to be that conventional systems are not adequatelyable to take into consideration significant tribologic characteristicsof the seal, like inertia, tiffness, frictional moment etc. As aconsequence, upon resetting of the torsional deformation or twist, thedeformation may not be sufficiently compensated.

The most readily observable result of these problems with conventionalsystems is a detrimental leakage rate which tends to increase withincreasing speed of the shaft and thus with increasing speeds of therotor sealing ring because of the pumping effect of the spiral grooves.This leakage phenomenon tends to increase even more as a result of theincomplete restoration of the sealing ring following a torsionaldeformation as described.

The fact that, in the prior art system, a temperature-dependent anddifferential-pressure-dependent torsional deformation of the statorsealing ring is permissible and is in part caused by the arrangement ofthe polar moment of inertia of the stator sealing ring, so that thedescribed pressure distribution in the gap is necessary to reset it, hasa further drawback which is detrimental to the effective operation ofthe seal. The described twist requires, in accordance with the laws ofmechanics, that the mounting ring gap be significantly greater than thefunctional annular gap as is formed when the stator sealing ring hasundergone twisting and without consideration of the resetting of thetwist resulting from the pressure distribution in the pressurized gasgap. The dimensions of the mounting ring gap (mounting tolerance) andthe ratio of the mounting ring gap to the functional gap under thevarious operating conditions cannot be related to the resetting in mostinstances because the temperature dependent deformation and theresetting which is dependent upon the operating state of the sealingarrangement do not occur simultaneously and both must occur underconditions that a contact of the sealing surface of the rotor and statorsealing rings does not occur.

In practice, under all conventional diameter relationships of thesealing arrangement in the conventional system, the width of themounting ring gap is in the range of 0.4 to 0.5 mm and usually,therefore, is in excess of 0.4 mm.

In practice that has meant that the O-ring of the conventional deviceshould have a corresponding hardness, for example, a Shore A hardness of90 or more in accordance with German Industrial Standards DIN 53505.

In spite of this adaptation of the O-ring to the conditions described,it has been found that operating pressure differentials above 80 bar orreaching a maximum of 100 bar cannot be provided in a practical sense ifthe sealing assembly is to be used for the conventional operating lifeof several thousand hours.

On the other hand, the industrial need is increasing for sealingarrangements which require much higher operating pressure differentials,i.e. pressure differentials which can be well above 100 bar. There isanother aspect of the operation of a conventional sealing of the typedescribed which should be mentioned. If one applies an O-ring of highhardness ahead of the annular gap between the stator sealing ring andthe cylindrical portion of the sealing housing, the latter is subjectedto nonuniform stresses resulting from the fact that the relativerotation of the shaft with the rotor sealing ring and the surroundinghousing is neither perfectly round nor perfectly coaxial with the statorsealing ring and the associated housing parts. Accordingly, vibrationscan result as induced by the stator sealing ring. These vibrations applyto the O-ring.

The functional annular gap must be defined with a certain amount of playto accommodate these vibrations without detriment to the sealingeffectiveness. When the O-ring is composed of a very hard material it isnot generally able to follow the induced movements of the stator sealingring and thus maybe unduly stressed and can become damaged. It may, ifhard enough, limit the play required as described above and resulting ina detriment to the sealing effectiveness. In particular, this can leadto detrimental contact between the sealing end faces of the rotorsealing ring and the stator sealing ring.

OBJECTS OF THE INVENTION

It is the principal object of the present invention to produce apressurized gas contactless sealing arrangement of the general typedescribed which will extend the principles set forth in our earlierapplications as identified above.

Another object of this invention is to provide a pressurized gas sealhaving a rotor sealing ring and a stator sealing ring and adapted toseal around a shaft which can avoid drawbacks of earlier systems andparticularly the earlier systems described above.

Yet another object of this invention is to provide a contactless sealarrangement, hereinafter referred to as a gas seal, a contactless sealor a pressurized gas seal, which can be used for operating differentialpressures significantly higher than those of earlier seals of this type,e.g. for operating pressure differences up to 300 or even to 500 bar,with more reliable and greater sealing effectiveness and longer usefulor operating life.

SUMMARY OF THE INVENTION

This object is achieved, in accordance with the invention, by providingthe stator sealing ring so that it also is developed of a hard sealingmaterial of high thermal conductivity, high modulus of elasticity andhigh hardness and, indeed, such that the stator sealing ring and therotor sealing ring are both composed of a hard sealing material of athermal conductivity in excess of 70 W/mK (=kJ/mhK), a modulus ofelasticity in excess of 250,000 N/mm² with corresponding hardness, apore volume of less than 1% and a surface roughness of less than 0.3 μum(Ra), preferably less than 0.03 μum (R_(a)).

According to another essential feature of the invention, the polar orgeometric moment of inertia of the stator sealing ring is sufficientlylarge that the gap width of the functional annular gap between theshaft-side cylindrical part of the sealing ring in the operational stateand under the operational differential pressure corresponds to thestructurally predetermined gap width of the mounting ring gap betweenthe cylindrical part of the sealing housing and the stator sealing ringin all operational states and is less than 0.4 mm and preferably lessthan 0.3 mm.

The third essential feature of the present invention is that the sealingO-ring additionally serve as a compensation or centering ring and, forthis purpose, has a material hardness which is greater than theextrusion threshold of this material through the gap and for the givengap width at the predetermined operating pressure differential and isless than a hardness of 90 Shore A according to German IndustrialStandard DIN 53 505. Preferably the hardness of the O-ring is less than80 Shore A under this standard.

In other words according to the invention the parts are so related anddimensioned that the orientations of the sealing end faces of the rotorsealing ring and the stator sealing ring do not change in operation andpreferably are always parallel.

With a sealing arrangement in accordance with the invention,surprisingly, it is not necessary to lay out the grooves or recesses insuch manner as to provide a restoring force as has been the caseheretofore. Indeed, the recesses or grooves on the juxtaposed sealingfaces on the rotor and stator ring can be selected for optimaldevelopment of the gas pressure blocking the seal. Preferably, therecesses can be formed as gas-displacement spiral grooves. In thisconnection, however, it is possible to form the recesses or grooves aspressure generating recesses with damming edges.

The reference to spiral grooves, of course, is intended to definegrooves of such shape that they provide a displacement of gas in apredetermined direction in the gas dynamic sense. This gas displacementcan be used to counteract the leakage flow which can give rise to theleakage rate of the fluid sealed by the arrangement and hithertoconsidered to be unavoidable. Recesses with a damming edge, by contrastare elements in the gas dynamic sense which prevent or do not allow adefinitive displacement of the gas, but rather serve to block suchdisplacement and create static gas pressure conditions.

In both cases, however, the invention allows optimization of the sealingeffect and this optimization is not adversely effected by the need togenerate a restoring force or the need to establish equilibriumcontinuous between a restoring force and a torsional force upon asealing ring.

In a preferred embodiment of the invention, stator sealing ring has apolar moment of inertia which limits temperature dependent torsionaldeformation of its sealing surface.

Such a polar moment of inertia can be calculated readily using methodswhich have become conventional in modern computer analysis of mechanicalsystems.

A value Ra is the mean roughness as determined by German IndustrialStandard DIN 4768.

In a preferred feature of the invention the planarity of the sealingsurface at room temperature and with a temperature gradient of zeroshould be 0.4 micrometers per 100 mm along the diameter.

In spite of the fact that the aforedescribed values of the thermalconductivity, modulus of elasticity and hardness are observed, thesealing rings can be composed of a variety of materials.

The sealing rings can be composed, for example, of a material selectedfrom the group which consists of tungsten carbide, silicon carbide,silicon/silicon carbide composites, titanium carbide, Si₃ N₄, Al₂ O₃ andZrO₂ or combinations, pairings and mixtures thereof.

The sealing rings can be formed by sintering or combinations of pressingand sintering allowing the pore volume of the sealing rings to beestablished.

In accordance with a feature of the invention, both sealing rings can becomposed of the same material. However, it is also possible to make thestator sealing ring on the one hand and the rotor sealing ring on theother from pairs of different materials within the compositions definedabove.

Best results are achieved, in accordance with the invention byfabricating the sealing rings so that their pore volumes are less than0.5%.

The stator sealing ring preferably can have an annular cross sectionwhose ring height in the axial direction is at least twice the radialring breadth.

With respect to the arrangement of the recesses, a preferred embodimentof the invention has the recesses or grooves beginning at a periphery ofthe respective sealing end face and terminating at a boundary betweenthe annular portion of the end face further with the grooves and agroove or recess free portion of the end face.

The recesses can start, in addition, from the inner diameter orcircumference or from the outer diameter or circumference of the sealingend face and can end at a recess-free dam.

In this latter case, the spiral grooves can be so arranged that thepumping effects of the two grooves are counter to one another.

Especially for the embodiment in which damming edges are provided, ithas been found advantageous to have the recesses terminate at ameander-shaped dam. According to the invention, moreover, the sealingend faces can be formed with emergency contacting layers in the form ofa coating or layer of several micrometers of graphite,polytetrafluoroethlene or a like, low-friction, low-wear material. Theprotective substance, reducing deterioration of the sealing surface uponemergency contact of one surface with the other, can also be carbonembedded in the material of the sealing surface.

In accordance with the invention, the embodiments wherein the recessesare formed with damming edges have proved to be of special significance.In a preferred embodiment in accordance with this aspect of theinvention, the damming edges of the recesses run in radial direction.Alternatively, the damming edges can be formed as circular arc segmentsas seen in an elevational view and this configuration has been found tobe most applicable where the recesses themselves are generally circular.

According to another feature of this aspect of the invention, thedamming edges can be lateral edges of recesses which are triangular intheir elevational view and which converge toward one of the peripheriesat which the recesses open, the triangle vertex being truncated at theperiphery.

The recesses according to the invention should be symmetrical withrespect to a line of symmetry extending in the radial direction. If thissymmetry requirement is fulfilled, the gas sealing arrangement of theinvention is independent of the direction of rotation of the shaft. Ifthis symmetry requirement is not fulfilled or is undesirable, therecesses can have asymmetrical damming edges which are, for example,L-shaped. The depths of the recesses can lie in the micrometer range.

The invention achieves all of the objects set forth above and thus hasthe advantage that a gas seal arrangement exploits a combination oftribiological characteristics and has its recesses so arranged that thegeneration of a moment or torque for resetting the torsionaldeformations need not be generated by the pressure distribution in thesealing gap.

While the recesses can be spiral grooves capable of a defined pumpingeffect, as a general matter the use of recesses with such a definitivepumping effect can be eliminated and, of course, this is the case withembodiments having damming edges which preclude a pumping action. Theelimination of the pumping effect substantially reduces the leakagerate.

If one compares the sealing arrangement of the invention prior art gasseals, it is found, quite surprisingly, that the leakage rate can bereduced by at least 50%. Associated with this is the possibility ofoperating the sealing rings at substantially higher temperatures becauseimmediately after startup there is a low temperature gradient so thattorsional deformations resulting from high temperature gradientspractically do not arise.

The temperature gradient in the axial direction lies below 1° C. ascompared to temperature gradients of 20° C. more with the prior artsystems. These advantages apply to all conventional sizes of the gassealing arrangement, i.e. shaft diameters of, for example, 50 to 250 mmand shaft peripheral speeds of up to 150 meters per second.

The polar moment of inertia of the stator sealing ring restrictstorsional deformation thereof. The low pore volume and the low surfaceroughness in the regions of the end faces of the sealing rings in whichthe recesses are not provided, appear to contribute substantially to areduction in the leakage rate.

Surprisingly, moreover, there are no startup and shutdown problems. Thelow incidence of startup and shutdown problems appears to be a result ofthe fact that the mounting tolerance is equal to the gap width of thefunctioning annular gap between the stator sealing ring and thecylindrical portion of the housing on which the stator sealing ring ismounted in practically all operating conditions and further that the gapwidth of the functional annular gap is substantially constant under allof these conditions.

Moreover, the functional gap width is so minimal that it can be bridgedby an O-ring of significantly reduced material hardness without raisinga danger of extrusion of the O-ring by the operating pressuredifferential. The sealing arrangement of the invention, therefore, canbe used for especially high pressure seals and operates with highreliability for an especially long useful life.

The assembly can comprise:

a sealing housing surrounding an axis;

a shaft extending along the axis and surrounded by the housing, theshaft being rotatable relative to the housing, the sealing housing beingformed with a cylindrical portion at a shaft side of the housingcoaxially surrounding the shaft;

a stator sealing ring extending around and axially overlapping thecylindrical portion, mounted on the housing and having an end facedefining one of a pair of sealing-gap-defining faces and composed of ahard sealing material of high thermal conductivity, high hardness andhigh modulus of elasticity, the stator sealing ring defining with thecylindrical portion and around the cylindrical portion a functionalannular gap and the stator sealing ring being movable axially on thecylindrical portion;

an O-ring composed of rubber or plastic bridging between the statorsealing ring and the cylindrical portion and axially sealing thefunctional annular gap;

a rotor sealing ring mounted on the shaft, rotatable entrained by theshaft and formed with an end face juxtaposed with the end face of thestator sealing ring defining another of the pair of sealing-gap-definingfaces and composed of a hard sealing material of high thermalconductivity, high hardness and high modulus of elasticity, the endfaces defining an annular sealing gap between them, relative rotation ofthe end faces generating a gas pressure in the sealing gap blockingpassage of fluid past the assembly; and

spring means including at least one spring braced between the housingand the stator sealing ring and applying to the stator sealing ring apredetermined axial force acting in a direction opposite the action ofthe gas pressure in the sealing gap on the stator sealing ring,

the stator sealing ring having a polar moment of inertia sufficient tomaintain a gap width of the functional annular gap substantially equalto a mounting tolerance of the stator sealing ring on the cylindricalportion in all operating conditions of the assembly and under anoperating pressure differential across the assembly,

the end face of the stator sealing ring and the end face of the rotorsealing ring having the same orientations with respect to one another inall operating conditions of the assembly,

the O-ring forming a position-compensating centering ring for the statorsealing ring on the cylindrical portion and having a material hardnesswhich is greater than an extrusion limit of material hardness forextrusion of the O-ring into the functional annular gap at the gap widthand under the operating pressure differential,

the stator sealing ring and the rotor sealing ring being composed ofmaterials having a thermal conductivity in excess of 70 W/mK (=kJ/mhK),a modulus of elasticity in excess of 250,000 N/mm², a pore volume ofless than 1% and a surface roughness less than 0.3 μm Ra, preferablyless than 0.03 μm (Ra),

the tolerance and the gap width of the functional annular gap being lessthan 0.4 mm, and

the O-ring having a material hardness less than 90 Shore A (DIN 53 505).

Within the invention is, therefore, a gas-pressure contactlessshaft-sealing assembly, comprising:

a sealing housing surrounding an axis;

a shaft extending along the axis and surrounded by the housing, theshaft being rotatable relative to the housing, the sealing housing beingformed with a cylindrical portion at a shaft side of the housingcoaxially surrounding the shaft;

a stator sealing ring extending around and axially overlapping thecylindrical portion, mounted on the housing and having an end facedefining one of a pair of sealing-gap-defining faces and composed of ahard sealing material of high thermal conductivity, high hardness andhigh modulus of elasticity, the stator sealing ring defining with thecylindrical portion and around the cylindrical portion a functionalannular gap and said stator sealing ring being movable axially on thecylindrical portion;

an O-ring composed of a material selected from the group which consistsof rubber or and plastic bridging between the stator sealing ring andthe cylindrical portion and axially sealing the functional annular gap;

a rotor sealing ring mounted on the shaft, rotatably entrained by theshaft and formed with an end face juxtaposed with the end face of thestator sealing ring defining another of the pair of sealing-gap-definingfaces and composed of a hard sealing material of high thermalconductivity, high hardness and high modulus of elasticity, the endfaces defining an annular sealing gap between them generating uponrelative rotation of the end faces a gas pressure in the sealing gapblocking passage of fluid past the assembly, at least one of the facesbeing provided with an array of equispaced triangular recesses adjacentan outer periphery of one of the end faces and symmetrical withreference to respective radii from the axis and having vertices layingalong the outer periphery; and

spring means including at least one spring braced between the housingand the stator sealing ring and applying to the stator sealing ring apredetermined axial force acting in a direction opposite the action ofthe gas pressure in the sealing gap on the stator sealing ring,

the stator sealing ring and the rotor sealing ring being composed ofmaterials having a thermal conductivity in excess of 70 W/mK (=kJ/mhK),a modulus of elasticity in excess of 250,000 N/mm², a pore volume ofless than 1% and a surface roughness less than 0.3 μm Ra,

the stator sealing ring having a geometric moment of inertia sufficientto maintain a gap width of the functional annular gap substantiallyequal to a gap width established upon assembly of the stator sealingring on the cylindrical portion in all operating conditions of theassembly and less than 0.4 mm, and

the O-ring forming a position-compensating centering ring for the statorsealing ring on the cylindrical portion and having a material hardnessless than 90 Shore A and greater than an extrusion limit of materialhardness for extrusion of the O-ring into the functional annular gap atthe gap width and 70 Shore A and under an operating pressuredifferential of substantially 300 to 500 bar.

Alternatively the invention is a gas-pressure contactless shaft-sealingassembly, comprising:

a sealing housing surrounding an axis;

a shaft extending along the axis and surrounded by the housing, theshaft being rotatable relative to the housing, the sealing housing beingformed with a cylindrical portion at a shaft side of the housingcoaxially surrounding the shaft;

a stator sealing ring extending around and axially overlapping thecylindrical portion, mounted on the housing and having an end facedefining one of a pair of sealing-gap-defining faces and composed of ahard sealing material of high thermal conductivity, high hardness andhigh modulus of elasticity, the stator sealing ring defining with thecylindrical portion and around the cylindrical portion a functionalannular gap and the stator sealing ring being movable axially on thecylindrical portion;

an O-ring composed of a material selected from the group which consistsof rubber or and plastic bridging between the stator sealing ring andthe cylindrical portion and axially sealing the functional annular gap;

a rotor sealing ring mounted on the shaft, rotatably entrained by theshaft and formed with an end face juxtaposed with the end face of thestator sealing ring defining another of the pair of sealing-gap-definingfaces and composed of a hard sealing material of high thermalconductivity, high hardness and high modulus of elasticity, the endfaces defining an annular sealing gap between them generating uponrelative rotation of the end faces a gas pressure in the sealing gapblocking passage of fluid past the assembly, at least one the end facesbeing formed with an array of equispaced circular recesses havingcircumferences osculating an outer periphery of one of the faces andsymmetrical with reference to respective radii from the axis; and

spring means including at least one spring braced between the housingand the stator sealing ring and applying to the stator sealing ring apredetermined axial force acting in a direction opposite the action ofthe gas pressure in the sealing gap on the stator sealing ring,

the stator sealing ring and the rotor sealing ring being composed ofmaterials having a thermal conductivity in excess of 70 W/mK (=kJ/mhK),a modulus of elasticity in excess of 250,000 N/mm², a pore volume ofless than 1% and a surface roughness less than 0.3 μm Ra,

the stator sealing ring having a geometric moment of inertia sufficientto maintain a gap width of the functional annular gap substantiallyequal to a gap width established upon assembly of the stator sealingring on the cylindrical portion in all operating conditions of saidassembly and less than 0.4 mm, and

the O-ring forming a position-compensating centering ring for the statorsealing ring on the cylindrical portion and having a material hardnessless than 90 Shore A and greater than an extrusion limit of materialhardness for extrusion of the O-ring into the functional annular gap atthe gap width and 70 Shore A and under an operating pressuredifferential of substantially 300 to 500 bar.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features and advantages of my inventionwill become more readily apparent from the following description,reference being made to the accompanying highly diagrammatic drawing inwhich:

FIG. 1 is an axial section through a sealing assembly of the presentinvention in the mounted state;

FIG. 2 is an elevational view of the rotor sealing ring of FIG. 1;

FIG. 3 is a view similar to FIG. 1 illustrating an embodiment of theinvention in which the T-shaped recesses extend inwardly on the rotorsealing ring from both of the peripheral edges of the rotor sealingring;

FIG. 4 is a view similar to FIG. 2 of an embodiment in which the dammingedges are circular arcs;

FIG. 5 is a view similar to FIG. 2 wherein the damming edges areinclined flanks of generally triangular recesses which are truncated atone vertex;

FIG. 6 is a view similar to FIG. 2 wherein the recesses have a spiralgroove configuration;

FIG. 7 is a view similar to FIG. 6 illustrating another embodiment;

FIG. 8 is an enlarged cross sectional detailed view of FIG. 1 in theregion of the sealing end faces;

FIG. 9 is a detailed section in the region of the functional gap;

FIG. 10 is a graph illustrating a feature of the invention;

FIG. 11 is a view similar to FIG. 8 showing another embodiment of theinvention;

FIG. 12 is a view of the end faces of the stator sealing ring of theembodiment of FIG. 11, illustrating a modification thereof; and

FIG. 13 is a cross sectional view illustrating another feature of theinvention.

SPECIFIC DESCRIPTION

The sealing arrangement illustrated in FIGS. 1 to 7 is provided for ashaft 1 and comprises a sealing housing 2 in which a stator sealing ring3 is mounted. As can be seen from FIG. 1, the sealing housing 2, inturn, is received in a housing 20 with respect to which the shaft 1 canbe journaled, e.g. of a compressor, pump or other device which must havea high pressure seal between regions having a high gas pressuredifferential there across. An O-ring 21 is provided in a groove 22 ofthe housing 2 and sealingly engages a surface of the housing 20. Thehousing 20 is provided with splines 23, for example, which are engagedin the grooves (not shown) of the housing 1 so that the latter cannotrotate relative to the housing 20. The housing 2 is also axially bracedagainst a shoulder 24 of the housing 20.

The housing 2 also has a cylindrical portion 25 which extends axiallyclose to the shaft 1 and closely surrounds the latter.

A stator sealing ring 3 is mounted on the housing 2 and has acylindrical surface 30 juxtaposed with the cylindrical surface 26 of thehousing to define a functional annular gap F whose gap width issubstantially equal to the mounting clearance of the stator sealing ring3 on the cylindrical portion 25.

The stator sealing ring 3 has a sealing end face 3a, a rear surface 31and an outer conical flank 32 extending between the rear end face 31 andthe sealing end face 3a. A further conical surface 33 of the sameconicity as the surface 32 extends between the end face 3a and thecylindrical surface 30.

The sealing end face 3a of the stator sealing ring is juxtaposed with asealing end face 4a of a rotor sealing ring 4. The rotor sealing ring 4is axially entrained with the shaft 1 via a sleeve 40 which has anaxially extending recess 41 in which a pin 42 from a shoulder 1a of theshaft engages to rotationally lock the sleeve 40 to the shaft. An O-ring43 in a groove 44 of the sleeve 40 seals this sleeve against the shaft.The sleeve 40 is clamped against the shoulder 1a by a clamping nut 45which is threadedly engaged on a threaded portion 1b of the shaft 1. Acylindrical portion 46 of the sleeve 40 receives the sealing ring 4which is sealed against the sleeve via O-rings 47 and 48. A pin 49 fromthe sleeve 40 engages in a hole 50 to insure that the rotor sealing ring4 will rotate with the sleeve 40 and hence with the shaft. A spacessleeve 51 is clamped between the ring 4 and the nut 45 and holds thering 4 against the O-ring 47.

The rotor sealing ring 4 is formed on its end face 4a with recesses 5which open along the periphery so as to develop a gas pressure in asealing gap 6 between the end faces 3a and 3b. This sealing gap has notbeen illustrated in FIG. 1 because of the square of the drawing but isreadily visible in FIG. 8.

A predetermined force is applied to the stator sealing ring 3 by aspring means constituted by a plurality of angularly equispaced coilsprings 7 received in respective pockets 7a of the housing 2 and bracedagainst a pressure ring 7b bearing upon the end face 31 of the statorsealing ring 3. The springs 7 thus press the stator sealing ring axiallyin the direction of the rotor sealing ring.

The stator sealing ring 3 has a ring height 8 which is greater than theradial breath 9 of the sealing end face 3a and is movably mounted, i.e.can move radially within the mounting tolerance limit relative to thehousing 2 and can be displaced axially by the spaces 7 or the pressurein the gap.

Both sealing rings 3 and 4 are composed of a material of high thermalconductivity, high modulus of elasticity, low pore volume and lowsurface roughness. Specifically, the thermal conductivity should exceed70 W/mK, the modulus of elasticity should exceed 250,000 N/mm² withcorresponding hardness, the pore volume should be less than 1% and thesurface roughness should be below 0.3 micrometer Ra, preferably below0.03 micrometer Ra.

The stator sealing ring 3 has an axial polar moment of inertia whichlimits temperature dependent torsional deformations of its sealing endface 3a. This can be seen from FIG. 1.

The recesses 5 can have configurations as shown in FIGS. 2 through 7.With the configurations of FIGS. 2 and 3, the recesses are shown to havebeen provided without concern for the formation of a restoring torquewhich would have to act counter to a torsional deformation and whichwould result from the pressure generated in the gap 6; with theseconfigurations the leakage rate is minimized. The damming edges 5acounteract any pumping effect. In FIGS. 2 and 3, the recesses aregenerally T-shaped and have radial damming edges 5a. In FIG. 4 therecesses 5 are generally circular. In FIG. 5 the recesses havetriangular configurations with uniformly truncated vertices. The sealingrings are composed of tungsten carbide, silicon carbide, silicon/siliconcarbide composites, titanium carbide or combinations or mixtures thereofpreferably of the same materials.

From FIGS. 2, 4 and 5, it is apparent that the recesses 4 and 5 can openalong the outer peripheral edge of the sealing end face 4a and canterminate at a dam 10 of the end face 4a which is formed by a portion ofthis end face free from recesses.

From FIG. 3 it can be seen that the recesses 5 can open at the innercircumference as well as at the outer circumference or periphery andthat the recesses, regardless of which periphery that extend inwardlyfrom, terminate at a central recess, free dam 10. In FIG. 3 the dam 10extends in a meander pattern.

The sealing and faces 3a and 4a can be provided with emergencycontacting coatings of the small thicknesses of graphite,polytetrafluoroethlene or the like. These coatings are shown at 3b and4b in FIG. 13 and have not been illustrated in other FIGS. because ofthe scale of the illustration.

With the embodiment of FIGS. 6 and 7, the recesses 5 are spiral grooves.In this case, a pumping effect is counteracted by having the groovesterminate at dams in the manner described.

FIG. 8 shows the gap region 6 to an enlarged scale. It will be apparentfrom this FIG. that the two sealing end faces 3a and 4a are, with greatprecision, planar and parallel to one another. In the operatingcondition of the sealing arrangement they define the sealing gap 6 whichcan be considered to be a fast or rigid gap and this gap is maintainedby the gas pressure within the gap acting counter to the springs 7.

From FIG. 1 it will be apparent that the functional annular gap Fcoincides substantially with the mounting ring gap or clearance requiredfor allowing the stator sealing ring 25 3 to be mounted on thecylindrical portion 25.

In operation, the width of this gap is held at a constant value,preferably of 0.4 mm or less and, still more advantageously, at 0.3 mmor less. Under all operating conditions, the stator sealing ring 3remains twist free.

The enlargement of FIG. 9 shows that an O-ring 11 in a groove 11' of thestator sealing ring 3 bridges the functional ring gap F and that therelative sizes of the O-ring and the gap width are such that even withvery high pressure differentials across the O-ring, the O-ring cannot beforced into or extruded through the functional gap F.

The O-ring 11 can, because of the small width of the functional annulargap 11, have a relatively low material hardness, i.e. a hardness of lessthan Shore A 90 and preferably less than a Shore A hardness of 80according to German Industrial Standard DIN 53 505.

As a consequence, the O-ring can serve as a centering element for thestator sealing ring 3 in the radial direction because it can have anappropriate elasticity for this purpose.

The spring 7 can be replaced by a closed bellows type spring which canfunction as a centering element.

In the embodiments of FIGS. 1 to 7, the sealing ring end face 4a of therotor sealing ring 4 and the sealing ring end face 3a of the statorsealing ring 3 are planar with a high degree of precision and parallelto one another.

In the embodiment of FIG. 11, however, which corresponds to FIG. 8 buthas a different configuration of the end face of the stator sealingring, the end face is here shown to comprise two annular surfaces 3a and3a' which adjoin one another at an edge 12 in a peak configuration.These annular surfaces are thus inclined to one another.

As can be seen from FIG. 12, instead of defining an edge, the peakregion between the surfaces 3a and 3a' can define a step 12'.

The invention utilizes configuration, materials and construction of thestator sealing ring and the rotor sealing ring such that no detrimentaltemperature dependent twist or other operation condition dependentdeformations of the stator sealing ring will occur.

That permits very small mounting tolerances to be used and, inparticular, a mounting tolerance which corresponds to the functionalannular gap F, the latter being small enough to operate with O-rings 11which are not destroyed, damaged or extruded into the functional annulargap by pressure differences of 300 to 500 bar or more. As a result, thesealing arrangement of the invention is suitable for high and very highpressures, has a minimum leakage rate and an extremely high useful life.

FIG. 10 is a diagram in which the characteristic of an O-ring disposedadjacent a gap and subjected to a high pressure is plotted.

Along the ordinate, we have plotted the operating pressure, i.e. thepressure differential across the O-ring tending to drive it into thegap, in bars. The abscissa axis has the radial gap width plottedtherealong.

The curves 70, 80 and 90 in this graph are labelled with the Shore Ahardness of the O-ring. All other conditions, namely, the size, closeface and diameter of the O-rings are the same.

The curves show, therefore, for each Shore A hardness of the O-ring theoperating pressure which will cause the O-ring to extrude into the gapof the corresponding width.

It has been found to be advantageous, as noted, to operate with a ShoreA hardness of 80 or less since greater hardness does not provide therequisite resiliency for centering of the stator sealing ring.

In FIG. 13, as noted, the end faces of the sealing rings 3 and 4 areshown to be provided with the layers 3b and 4b of the friction reducingsubstances.

We claim:
 1. A gas-pressure contactless shaft-sealing assembly,comprising:a sealing housing surrounding an axis; a shaft extendingalong said axis and surrounded by said housing, said shaft beingrotatable relative to said housing, said sealing housing being formedwith a cylindrical portion at a shaft side of said housing coaxiallysurrounding said shaft; a stator sealing ring extending around andaxially overlapping said cylindrical portion, mounted on said housingand having an end face defining one of a pair of sealing-gap-definingfaces and composed of a hard sealing material of high thermalconductivity, high hardness and high modulus of elasticity, said statorsealing ring defining with said cylindrical portion and around saidcylindrical portion a functional annular gap, said stator sealing ringbeing movable axially on said cylindrical portion; an O-ring composed ofa material selected from the group which consists of rubber and plasticbridging between said stator sealing ring and said cylindrical portionand axially sealing said functional annular gap; a rotor sealing ringmounted on said shaft, rotatably entrained by said shaft and formed withan end face juxtaposed with said end face of said stator sealing ringdefining another of said pair of sealing-gap-defining faces and composedof a hard sealing material of high thermal conductivity, high hardnessand high modulus of elasticity, said end faces defining an annularsealing gap between them generating upon relative rotation of said endfaces a gas pressure in said sealing gap blocking passage of fluid pastsaid assembly, at last one of said end faces being provided with anarray of equispaced triangular recesses adjacent an outer periphery ofsaid one of said end faces and symmetrical with reference to respectiveradii from said axis and having vertices lying along said outerperiphery; and spring means including at least one spring braced betweensaid housing and said stator sealing ring and applying to said statorsealing ring a predetermined axial force acting in a direction oppositethe action of said gas pressure in said sealing gap on said statorsealing ring, said stator sealing ring and said rotor sealing ring beingcomposed of materials having a thermal conductivity in excess of 70 W/mK(=kJ/mhK), a modulus of elasticity in excess of 250,000 N/mm², a porevolume of less than 1% and a surface roughness less than 0.3 μm Ra, saidstator sealing ring having a geometric moment of inertia sufficient tomaintain a gap width of said functional annular gap substantially equalto a gap width established upon assembly of said stator sealing ring onsaid cylindrical portion in all operating conditions of said assemblyand less than 0.4 mm, and said O-ring forming a position-compensatingcentering ring for said stator sealing ring on said cylindrical portionand having a material hardness less than 90 Shore A and greater than anextrusion limit of material hardness for extrusion of said O-ring intosaid functional annular gap at said gap width and 70 Shore A and underan operating pressure differential of substantially 300 to 500 bar. 2.The assembly defined in claim 1 wherein said surface roughness is lessthan 0.03 μm Ra.
 3. The assembly defined in claim 1 wherein saidtolerance and said gap width of said functional annular gap is less than0.3 mm.
 4. The assembly defined in claim 1 wherein said O-ring has amaterial hardness less than 80 Shore A.
 5. The assembly defined in claim1 wherein said rotor sealing ring and said stator sealing ring are eachcomposed of a material selected from the group which consists oftungsten carbide, silicon carbide, silicon/silicon carbide composite,titanium carbide and mixtures, pairings and combinations thereof.
 6. Theassembly defined in claim 1 wherein said end faces have a planarity of0.4 micrometer/100 mm of diameter at room temperature and a zerotemperature gradient thereacross.
 7. The assembly defined in claim 1wherein said stator sealing ring and said rotor sealing ring have porevolumes of less than 0.5%.
 8. The assembly defined in claim 1 whereinsaid stator sealing ring has an axial length at least twice a radialwidth thereof.
 9. The assembly defined in claim 1 wherein said end faceof said stator sealing ring is composed of at least two annular surfacesadjoining at an annular edge.
 10. The assembly defined in claim 1wherein said end face of said stator sealing ring is composed of atleast two frustoconical annular surfaces adjoining at an annular peakededge.